The embodiments of the invention are directed to a method for detecting defective injection nozzles for delivering fuel into the combustion chambers of an internal combustion engine, in particular in a motor vehicle, as well as a suitable engine test device for detecting defective injection nozzles.
Internal combustion engines with direct injection include injection nozzles for the fuel supply to the individual combustion chambers in the cylinders. The injection nozzles ensure that the target mixture quality (air-fuel ratio) is suitably adjusted according to the requirements of the engine mode.
Injection nozzle defects in internal combustion engines are often hard to identify in the installed state of the injection nozzles. Consequently, in the event of malfunctions of an internal combustion engine, the cause of which could lie in defective injection nozzles, the nozzles are often replaced on suspicion. In many cases this results in the erroneous replacement of injection nozzles without defects. As a consequence, repeated repairs are necessary. Furthermore, the warranty costs of the engine manufacturer increase owing to unnecessary repairs.
It is an object of the embodiments of the invention to provide a method and a suitable engine test device, with which injection nozzle defects can be reliably detected with an indication regarding the type of the defect without having to remove the injection nozzles from the internal combustion engine.
This and other objects are achieved by a method for detecting defective injection nozzles for delivering fuel into the combustion chambers of an internal combustion engine, in particular in a motor vehicle. The internal combustion engine includes one or more cylinder banks, in which a respective cylinder bank includes a plurality of cylinders, each with a combustion chamber formed therein and at least one injection nozzle. In a preferred embodiment, exactly one injection nozzle is provided in each combustion chamber. A common air mass flow is delivered into the combustion chambers of a respective cylinder bank. Likewise, a common exhaust gas flow is discharged from the combustion chambers of a respective cylinder bank.
A number of consecutive test steps may be carried out for a respective cylinder bank in the idle mode of the internal combustion engine. The number of the test steps may be greater than the number of cylinders of the respective cylinder bank. This is necessary because otherwise the equation system described further below cannot be uniquely solved. In a respective test step, mixture factors are set for the individual injection nozzles that determine the respective fuel mass flow through the individual injection nozzle that is produced when the nozzle is actuated, in which for at least some, and in particular all, consecutive test steps one or more mixture factors are changed from one test step to the next and in which measurements of the lambda value of the exhaust gas flow discharged from the cylinder bank (for example by means of a lambda probe) and measurements of the air mass flow supplied to the cylinder bank are carried out during the test steps. The masses can be accounted for using the measurement of air mass (inwards) and the exhaust gas lambda (outwards). The changes of the mixture factors are in particular selected so that the system of equations described below has a unique solution. The lambda value term (also referred to as the air-fuel ratio) is determined and describes the air-fuel ratio in relation to the fuel-specific stoichiometric air-fuel ratio.
After performing the number of test steps, a standard deviation value for each injection nozzle as well as a total leakage flow are determined. The standard deviation value for a respective injection nozzle describes a deviation of the fuel mass flow produced by the respective injection nozzle from a standard operating value of the respective injection nozzle. The standard operating value of an injection nozzle means here and below the value of the fuel mass flow produced by an intact injection nozzle at the current operating point. In contrast, the total leakage flow describes the fuel mass flow that is caused by the leakage of all the injection nozzles of the respective cylinder bank.
In the method according to the invention, the determination of the standard deviation values for the respective injection nozzles and of the total leakage flow is carried out so that a system of equations that includes an equation for a respective test step can be solved by a computer. The equation accounts for the standard deviation values and the total leakage flow depending on: the mixture factors set in the respective test step, a lambda value of the exhaust gas flow discharged from the cylinder bank that is valid for the respective test step and that is derived from the measurements of the lambda value, and an air mass flow that is delivered to the cylinder bank that is valid for the respective test step and that is derived from the measurements of the air mass flow.
The lambda value or the air mass flow that is valid for the respective test step can be derived differently from the corresponding measurements depending on the configuration of the method. If a plurality of measurements of the lambda value or of the air mass flow are carried out in an individual test step, the valid lambda value or air mass flow in the respective test step can be determined by averaging the measurement values. In relation to the air mass flow, it can also be assumed therefrom that the air mass flow remains constant within the number of test steps, so that an air mass flow that is valid for all test steps is used that constitutes an average of the measurement values of the air mass flow across all the test steps. It may also be possible that the air mass flow or the lambda value is only ever measured once in an individual test step. The valid values in the respective test step then coincide with the corresponding measured values.
After the standard deviation values and the total leakage flow have been determined, in the method according to the invention a first injection nozzle defect in the respective cylinder bank in the form of an injection quantity deviation of at least one injection nozzle is detected if at least one standard deviation value for a respective injection nozzle lies outside a predefined range of values. Furthermore, a second injection nozzle defect is detected in the respective cylinder bank in the form of a leak of at least one injection nozzle if the total leakage flow is greater than the predefined threshold value or the maximum value thereof. Suitable ranges of values or threshold values can easily be determined by a person skilled in the art. Preferred values for the threshold value or the range of values are to be found in the specific description. A detected first or second injection nozzle defect is preferably output by means of a user interface or placed in a suitable digital memory for subsequent read-out.
The method according to the invention has the advantage that in a simple way by multiple adjustment of the fuel mixture, not only can injection nozzle defect be detected, but it can also be distinguished whether the fault indicator of the defect is in the form of an injection quantity deviation and/or a leak. An injection quantity deviation is distinguished from a leak defect in that the injection quantity deviation only occurs when the injection nozzle is turned on (i.e. during the injection of fuel through the nozzle), whereas the leak is also present if the injection nozzle is turned off and no fuel should be being injected.
In a preferred embodiment, within the method according to the invention an output can also be provided indicating for which injection nozzles the standard deviation value lies outside the predefined range of values. The injection nozzles are detected as defective. In this way, the association of the injection quantity deviation defect with the corresponding injection nozzles is achieved. The output of injection nozzles with a standard deviation value outside the predefined range of values can for example be carried out by means of a user interface. An output can also mean storing the corresponding information in a digital memory that can be analyzed at a later point in time.
In a preferred embodiment, each of the above standard deviation values is a percentage factor that is produced by multiplication of the fuel mass flow produced through the respective injection nozzle by the standard operating value. In a further preferred embodiment, each of the mixture factors represents a mixture trim in the form of a percentage factor that produces the actual fuel mass flow of the respective injection nozzle by multiplication with the fuel mass flow produced by the respective injection nozzle in the normal mode of the internal combustion engine. The normal mode of the internal combustion engine means the operation thereof without measurement intervention, i.e. without mixture trimming. In other words, the normal mode corresponds to a mixture trim with the percentage factor of 1 or 100%.
In a further configuration of the method according to the invention, a respective equation of the system of equations also includes a desired air-fuel ratio (i.e. a target air-fuel ratio) for fuel combustion in a combustion chamber. In a further version, a respective equation of the system of equations also includes a mixture adjustment parameter for each injection nozzle, which adjusts the fuel mass flow through the respective injection nozzle that is produced when the nozzle is actuated to achieve smooth running of the internal combustion engine. Such mixture adjustment parameters are known in the control of an internal combustion engine and can as a rule be read out of the engine control unit. Nonetheless, the method according to the invention can also be used for internal combustion engines that do not carry out mixture adjustment using a mixture adjustment parameter. The set of mixture adjustment parameters is then to be set equal to 1 or 100% in each case.
In a particularly preferred version of the method according to the invention, a respective equation of the system of equations reads as follows
                    ∑        i            ⁢              (                              gv            i                    ·                      cb            i                    ·                      o            i                          )              +                                        L            st                    ·                      λ            soll                    ·          M                MSHFM            ·              L                  0          ,          sum                      =      M          λ              real        ,        k            
in which i=1, . . . , M indexes the injection nozzles of the number of M injection nozzles of the respective cylinder bank;
in which gvi represents the mixture factors set in the corresponding test step in the form of a mixture trim, which is a percentage factor that produces the actual fuel mass flow through the respective injection nozzle by multiplication with the fuel mass flow produced by the respective injection nozzle in the normal mode of the internal combustion engine; in which all cbi are set to the value 1 or in which a respective cbi is a mixture adjustment parameter for a respective injection nozzle that adjusts the fuel mass flow generated through the respective injection nozzle when actuated to achieve smooth running of the internal combustion engine; in which oi is the standard deviation value for a respective injection nozzle that is a percentage factor that gives the fuel mass flow produced through the respective injection nozzle by multiplication with the standard operating value of the respective injection nozzle; in which Lst·λsoll is a target air-fuel ratio that is identical for all combustion chambers during fuel combustion in the combustion chamber and Lst is the stoichiometric air-fuel ratio and λsoll represents a target lambda value of the fuel combustion in the combustion chamber; in which MSHFM is the valid air mass flow of the entire cylinder bank for the respective test step; in which L0,sum is the total leakage flow of all injection nozzles of the cylinder bank; in which λreal,k is the valid lambda value for the respective test step.
In a further preferred version, the system of equations that is processed in the method is solved by means of a matrix calculation. A robust solution of the equations is ensured thereby. In order to obtain an accurate and unique solution for the system of equations, the mixture factors for the respective test steps are preferably set so that after performing the test steps, each injection nozzle produces no fuel mass flow at least once (i.e. is turned off), produces a fuel mass flow at least once that is greater than a fuel flow that is produced by the respective injection nozzle in the normal mode of the internal combustion engine (i.e. the nozzle injects too richly), and produces a fuel mass flow at least once that is less than a fuel mass flow produced by the respective injection nozzle in the normal mode of the internal combustion engine (i.e. the nozzle injects too leanly). In addition or alternatively, the mixture factors for the respective test steps are preferably set so that there is at least one test step in which all the injection nozzles produce a fuel mass flow that corresponds to the fuel mass flow that is produced by the respective injection nozzle in the normal mode of the internal combustion engine (i.e. the nozzles inject without being adjusted) and/or that a test step in which at least one injection nozzle is not producing any fuel mass flow is followed by a test step in which each injection nozzle produces a fuel mass flow. In this way it is ensured that the individual injection nozzles pass through all sections of the injection quantity characteristic curve thereof, so that the reliable detection of injection nozzle defects is guaranteed.
In a further version of the method according to the invention, in the case of the detection of a leak it is further possible to determine which of the injection nozzles has a leak. For this purpose, the following steps are carried out for each injection nozzle: the mixture factor for the respective injection nozzle is successively varied starting from a standard value corresponding to the fuel mass flow produced by the respective injection nozzle in the normal mode of the internal combustion engine up to values with an increased injected fuel proportion of the respective injection nozzle, whereas the mixture factors of the other injection nozzles are held at the standard value; the rough running of the internal combustion engine is measured (for a sufficiently long time) for the standard value and for each changed value of the mixture factor of the respective injection nozzle; the value of the changed mixture factor at which essentially the same rough running occurs as for the standard value of the mixture factor is determined as a target value of the changed mixture factor; if the target value lies outside a predetermined range of values that corresponds to the lambda values for the combustion chamber exhaust gas flow that are greater than a predefined threshold value, the respective injection nozzle is detected as defective, in which the combustion chamber exhaust gas flow is the exhaust gas flow of the individual combustion chamber in which the respective injection nozzle is disposed.
If the target value lies within the predetermined range of values, no leakage defect of the respective injection nozzle is detected. The detection of the rough running of internal combustion engines with suitable measurement methods is known and is therefore not described in detail. The embodiment described above makes use of the knowledge that excessively rich injection mixtures and hence leaks can be detected by means of a relationship of the rough running to the mixture injection. In a preferred version, the range of values predetermined above is determined by means of a predetermined function that models the relationship between the rough running value and the lambda value for the combustion chamber exhaust gas flow or the mixture factor for the respective injection nozzle. The predetermined function is preferably a parabola.
Besides the method described above, the invention further concerns an engine test device for detecting defective injection nozzles for delivering fuel into the combustion chambers of an internal combustion engine. The engine test device is arranged to carry out the method according to the invention or one or more preferred versions of the method according to the invention. The engine test device can for example be an external engine test device or may also be integrated within the motor vehicle.
The invention further concerns a motor vehicle with an internal combustion engine and injection nozzles for delivering fuel into the combustion chambers of the internal combustion engine, in which the motor vehicle includes the engine test device described above. Exemplary embodiments of the invention are described in detail below. Other objects, advantages and novel features of the embodiments of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings, in which: